The sunlight contains some kinds of light harmful to eyes and gives a sense of glare to the eyes. In general, sunglasses are used for controlling the transmission of sunlight and, therefore, produced under a design for decreasing the transmittance of light in the vicinity of the central wavelength on the standard relative visibility curve (FIG. 2) to reduce the glare. In the conventional sunglasses, however, the transmittance of light over the other range of wavelength is also decreased as shown in FIG. 3 as a result of decrease in light at the central wavelength of 555 nm. For this reason, when the sunglasses are used under the conditions that the amount of light is small such as in the twilight, the whole field of vision may become dark, and it may, therefore, be difficult to observe an object in the open air. In other words, the attempt at reducing the glare may result in an excessive decrease in the amount of transmitted light all over the range of wavelength, thereby causing a problem that the object cannot be fully observed.
As the sunglasses which can exhibit non-glaring effects by decreasing the transmittance of light in the vicinity of the central wavelength on the standard relative visibility curve, while retaining the lightness in the whole field of vision, there are well known sunglasses which are made of a glass material containing neodymium or didymium for absorption of light in the vicinity of 590 nm. From the viewpoint of easy handling, however, synthetic resins such as plastics, particularly polycarbonate with high impact resistance, rather than glasses are preferred as the base material. There has been, however, no plastic lens complying with such requirements, particularly made of polycarbonate. JP-B 53-39910 discloses a lens for eyeglasses, which can absorb light over a wide range of wavelength extending from 550 to 600 nm with good visibility. The lens of this type for eyeglasses is made of diethylene glycol bisallylcarbonate (CR-39) as the base material; however, if this material is made into polycarbonate, the resulting material will be difficult to be colored with a dye. Furthermore, the above lens for eyeglasses exhibits a gradual decrease in the transmittance of light over the wavelength range of about 550 to 650 nm (yellow to orange color). If the transmittance of yellow light is decreased for the purpose of enhancing non-glaring effects, the transmittance of orange light is also decreased with such a decrease. Therefore, when eyeglasses with such lenses are used by the improper method of use, for example, these lenses are hard to transmit orange light from sodium lamps (central wavelength, 589 nm) for illumination in a tunnel, and there is a possibility that the filed of vision may become dark.
On the other hand, it is well known that ultraviolet light or other light having potential influences on the eyes is emitted from a screen of the CRT such as those of a personal computer, a word processor or the like. In order to shut up such light, there has been used a filter attached to a front surface of the screen. As such a filter, there is a filter having an effect for preventing reflected light from the front surface of the screen. In addition, there is a filter that can cut off ultraviolet light, or reduce the transmittance over a wide range of visible light in order to reduce glare of the screen. In this respect, these functions are common to those of the conventional sunglasses which are used for controlling the transmission of the sunlight. Therefore, when the conventional filter for sunglasses with the transmittance curve as shown in FIG. 3 is used as the front surface of the CRT screen, there is a possibility that the whole field of vision may become dark, and an image of the CRP cannot be clearly perceived. Furthermore, when the filter for the CRT having an equivalent structure to that of the aforementioned lens for eyeglasses disclosed in JP-B 53-39910/1978 is made and used, the amount of whole transmitted light may excessively decreased where the CRT screen displays a colorful moving image such as today's television games, or a color contrast may be deteriorated and, thereby, in some cases, color may become hard to be discriminated and the object image cannot be clearly perceived.